Method for integrated circuit patterning

ABSTRACT

A method of forming a target pattern includes forming a plurality of lines over a substrate with a first mask and forming a first spacer layer over the substrate, over the plurality of lines, and onto sidewalls of the plurality of lines. The plurality of lines is removed, thereby providing a patterned first spacer layer over the substrate. The method further includes forming a second spacer layer over the substrate, over the patterned first spacer layer, and onto sidewalls of the patterned first spacer layer, and forming a patterned material layer over the second spacer layer with a second mask. Whereby, the patterned material layer and the second spacer layer collectively define a plurality of trenches.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs and, for these advances to be realized,similar developments in IC processing and manufacturing are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion.

FIG. 1 is a flow chart of a method of forming a target pattern or deviceon a substrate for implementing one or more embodiments of the presentdisclosure.

FIG. 2 illustrates an exemplary substrate and a target pattern to beformed thereon according to various aspects of the present disclosure.

FIGS. 3 a-14 b are top and cross sectional views of forming the targetpattern of FIG. 2 according to the method of FIG. 1, in accordance withan embodiment.

FIG. 15 illustrates a final pattern with various dimensions that can betuned according to various aspects of the present disclosure.

FIGS. 16 a-17 b are top and cross sectional views of forming mandrellines for the target pattern of FIG. 2 according to the method of FIG.1, in accordance with an embodiment.

FIGS. 18 a-18 b are top and cross sectional views of forming trenchesfor the target pattern of FIG. 2 according to the method of FIG. 1, inaccordance with an embodiment.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. In addition, the present disclosuremay repeat reference numerals and/or letters in the various examples.This repetition is for the purpose of simplicity and clarity and doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed. Moreover, the performance of a firstprocess before a second process in the description that follows mayinclude embodiments in which the second process is performed immediatelyafter the first process, and may also include embodiments in whichadditional processes may be performed between the first and secondprocesses. Various features may be arbitrarily drawn in different scalesfor the sake of simplicity and clarity. Furthermore, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

The present disclosure is generally related to using spacer techniquesto improve integrated circuit pattern density in advanced process nodes,such as 14 nanometer (nm), 10 nm, and so on, with 193 nm immersionlithography or other suitable lithographic technologies. In one spacertechnique, a photoresist material is patterned on a substrate and issubsequently trimmed. Then, the trimmed photoresist pattern istransferred to a mandrel layer below thereby forming mandrel lines andthe trimmed photoresist pattern is thereafter removed. A spacer isformed on the sidewalls of the mandrel lines. A subsequent spaceretching and mandrel removing process results in leaving the spacer onthe substrate as a final pattern. While the pitch of the final patternis reduced attributable to the photoresist trimming process, a lineend-to-end (EtE) distance of the final pattern is undesirably increasedby the same photoresist trimming process. This can be explained bynearly equal etching rates of the photoresist material at both thelateral and vertical directions. The present disclosure uses a doublespacer process to increase a final pattern density even without thephotoresist trimming process. An advantage of the present disclosure isthat the final pattern's pitch, line-to-line spacing and EtE distancecan be flexibly tuned by adjusting thickness of the spacers.

Referring now to FIG. 1, a flow chart of a method 100 for forming atarget pattern or device according to various aspects of the presentdisclosure is illustrated. Additional operations can be provided before,during, and after the method 100, and some operations described can bereplaced, eliminated, or moved around for additional embodiments of themethod. The method 100 will be further described below. The method 100is an example, and is not intended to limit the present disclosurebeyond what is explicitly recited in the claims.

FIG. 2 shows an exemplary target pattern 200. The target pattern 200includes dense features 180 a-b, 182 a-b, and 184 a-b, arranged in tworows, and an isolated feature 186. For the sake of example, the “b”features (180 b, 182 b, and 184 b) have the same dimensions and spacingas the “a” features (180 a, 182 a, and 184 a) respectively and all the“a” and “b” features have the same dimension L in Y direction. An end toend distance in Y direction between the “b” features and the “a”features, EtE, is a critical dimension of the target pattern 200. Thefeatures 180 a, 182 a, and 184 a have a width W₁, W₂, and W₃respectively in X direction. Furthermore, the features 180 a, 182 a, and184 a are spaced by spacing S₁ and S₂ in X direction. The target pattern200 may be used to form various features of an integrated circuit (IC).In an embodiment, the target pattern 200 is used to form metal lines ina multilayer interconnection structure. In another embodiment, thetarget pattern 200 is used to form a plurality of trenches in thesemiconductor substrate for shallow trench isolation (STI) features. Asthe density of integrated circuits increases, some features may be tooclose together for the resolution of a mask (or photo mask). To overcomethis issue, features of a target pattern can be assigned to two or moremasks. In the present embodiment, the features 180 a-b and 184 a-b areassigned to a first mask and the features 182 a-b and 186 are assignedto a second mask. As will be discussed below, the second mask includespatterns overlapping the features 180 a-b and 184 a-b with relaxedprecisions, using a spacer self-aligning technique. This point will bedetailed in a later section.

In the following discussion, the method 100 (FIG. 1) is described inconjunction with FIGS. 3 a-17 b to show how the target pattern 200 isformed using the first mask and the second mask according to variousaspects of the present disclosure. In each of the FIGS. 3 a-18 b, thefigure designated with the suffix “a” (e.g., FIG. 3 a) includes a dottedline that defines cross sectional views for the figures designated withthe suffix “b,” “c,” and so on (e.g. FIG. 3 b).

The method 100 (FIG. 1) receives a substrate 202 at operation 102.Referring to FIGS. 3 a and 3 b, in the present embodiment, the substrate202 includes material layers 214 and 216. The material layer 216 may useamorphous silicon (a-Si), silicon oxide, silicon nitride (SiN), or othersuitable material or composition. The material layer 214 may usenitrogen-free anti-reflection coating (NFARC), spin-on glass (SOG),titanium nitride, or other suitable material or composition. Thematerial layers 214 and 216 may be formed by a variety of processes. Forexample, the material layer 214 may be formed over another substrate bya procedure such as deposition. In an embodiment, the material layer 216may include silicon oxide formed by thermal oxidation. In an embodiment,the material layer 216 may include SiN formed by chemical vapordeposition (CVD). For example, the material layer 216 may be formed byCVD using chemicals including Hexachlorodisilane (HCD or Si₂Cl₆),Dichlorosilane (DCS or SiH₂Cl₂), Bis(TertiaryButylAmino) Silane (BTBASor C₈H₂₂N₂Si) and Disilane (DS or Si₂H₆). The material layers 214 and216 may be formed by a similar or a different procedure. The exemplarycompositions of the material layers 214 and 216 aforementioned do notlimit the inventive scope of the present disclosure.

The method 100 (FIG. 1) proceeds to operation 104 by forming mandrellines over the substrate 202 with the first mask through a suitableprocess, such as a process including a photolithography process.Referring to FIGS. 4 a and 4 b, mandrel lines 218 a-d are formed overthe substrate 202. The mandrel lines, 218 a, 218 c, 218 b and 218 d, aredefined in the first mask corresponding to the features 180 a-b and 184a-b (FIG. 2) respectively with a pitch P_(m). The mandrel lines 218 a-c(218 b-d) have a first dimension W_(1m) (W_(3m)) in X direction and asecond dimension L_(m) in Y direction. The dimensions W_(1m), W_(3m),and L_(m) are greater than the corresponding dimensions W₁, W₃ and L(FIG. 2) respectively. This point will become clearer in a later sectionin conjunction with FIG. 15.

In an embodiment, the mandrel lines 218 a-d are formed in a negative orpositive resist (or photoresist) material in a photolithography process.An exemplary photolithography process includes coating a negative resistlayer 218 over the material layer 216, soft baking the resist layer 218,and exposing the resist layer 218 to a deep ultraviolet (DUV) lightusing the first mask. The process further includes post-exposure baking(PEB), developing, and hard baking thereby removing unexposed portionsof the resist layer 218 and leaving exposed portions of resist layer 218on the substrate 202 as the mandrel lines 218 a-d. In anotherembodiment, the mandrel lines 218 a-d may be formed with unexposedportions of a positive resist material layer in a similarphotolithography process.

In another embodiment, the mandrel lines 218 a-d may be formed in a hardmask layer using a photolithography process followed by an etchingprocess. Referring to FIGS. 16 a-17 b, hard mask layers, 218(2) and 217,and a resist layer 219 are formed over the material layer 216. Theresist layer 219 is patterned with the first mask through aphotolithography process (FIGS. 16 a and 16 b), such as thephotolithography process discussed above. The hard mask layer 217 isetched through the openings of the patterned resist layer 219 and thepatterned resist layer 219 is thereafter removed using a suitableprocess, such as wet stripping or plasma ashing. The hard mask layer218(2) is subsequently etched using the patterned hard mask layer 217 asan etch mask and the hard mask layer 217 is thereafter removed, leavingthe mandrel lines 218 a-d in the hard mask layer 218(2) (FIGS. 17 a and17 b). In one example, etching the hard mask layer 217 includes applyinga dry (or plasma) etch to remove the hard mask layer 217 within theopenings of the patterned resist layer 219. For example, a dry etchingprocess may implement an oxygen-containing gas, a fluorine-containinggas (e.g., CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-containinggas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃), a bromine-containing gas(e.g., HBr and/or CHBR₃), an iodine-containing gas, other suitable gasesand/or plasmas, and/or combinations thereof. The hard mask layer 218(2)may be etched using a similar or a different etching process.

The method 100 (FIG. 1) proceeds to operation 106 by forming a firstspacer layer 220 over the substrate 202 and over and around the mandrellines 218 a-d. Referring to FIGS. 5 a and 5 b, the first spacer layer220 is formed over the substrate 202, more specifically, over thematerial layer 216. The first spacer layer 220 is also formed over themandrel lines 218 a-d and onto the sidewalls of the mandrel lines 218a-d. The first spacer layer 220 has a first thickness T₁. The firstspacer layer 220 includes one or more material or composition differentfrom the material layer 216 and the mandrel lines 218 a-d. In anembodiment, the first spacer layer 220 may include a dielectricmaterial, such as titanium nitride, silicon nitride, silicon oxide, ortitanium oxide. The first spacer layer 220 may be formed by a suitableprocess, such as a deposition process. For example, the depositionprocess includes a chemical vapor deposition (CVD) process or a physicalvapor deposition (PVD) process.

The method 100 (FIG. 1) proceeds to operation 108 by etching the firstspacer layer 220 to expose the mandrel lines 218 a-b and the materiallayer 216. Referring to FIGS. 6 a and 6 b, the top surfaces of themandrel lines 218 a and 218 b are exposed by this etching process andthe first spacer material disposed over the material layer 216 is alsopartially removed, providing first spacer features 220 a-d on thesidewalls of the mandrel lines 218 a-d respectively. In an embodiment,the process of etching the first spacer layer 220 includes ananisotropic etch such as plasma etch.

The method 100 (FIG. 1) proceeds to operation 110 by removing themandrel lines 218 a-d. Referring to FIGS. 7 a and 7 b, the mandrel lines218 a-d are removed, leaving the first spacer features 220 a-d over thesubstrate 202. The mandrel lines 218 a-d are removed using a processtuned to selectively remove the mandrel lines 218 a-d while the firstspacer features 220 a-d remain.

The method 100 (FIG. 1) proceeds to operation 112 by forming a secondspacer layer 222 over the substrate 202 and over and around the firstspacer features 220 a-d. Referring to FIGS. 8 a and 8 b, the secondspacer layer 222 is formed over the substrate 202, more specifically,over the material layer 216. The second spacer layer 222 is also formedover the first spacer features 220 a-d and onto the sidewalls of thefirst spacer features 220 a-d. The second spacer layer 222 has a secondthickness T₂. The second spacer layer 222 includes one or more materialor composition different from the material layer 216. The second spacerlayer 222 may use the same or different material or composition from thefirst spacer layer 220. However, the materials used in the two spacerlayers, 220 and 222, may have similar etch selectivity in order toprevent undesired micro-trench formation when the two spacer layers areetched in later steps. In an embodiment, the second spacer layer 222 mayinclude a dielectric material, such as titanium nitride, siliconnitride, silicon oxide, or titanium oxide. The second spacer layer 222may be formed by a suitable process, such as a deposition process. Forexample, the deposition process includes a chemical vapor deposition(CVD) process or a physical vapor deposition (PVD) process.

The method 100 (FIG. 1) proceeds to operation 114 by forming anothermaterial layer over the second spacer layer 222. Referring to FIGS. 9 aand 9 b, a material layer 224 is formed over the substrate 202 and overthe second spacer layer 222. In an embodiment, the material layer 224 isfirst deposited over the second spacer layer 222 and is then partiallyremoved such that the second spacer layer 222 over the top surfaces ofthe first spacer features, 220 a-d, are exposed. The partial removal ofthe material layer 224 may be done by a procedure, such as a chemicalmechanical polishing (CMP) or etch back. In an embodiment, the materiallayer 224 uses bottom anti-reflective coating (BARC) or spin-on glass(SOG).

The method 100 (FIG. 1) proceeds to operation 116 by forming trenchesonto the material layer 224 and the second spacer layer 222 with thesecond mask. This operation includes a variety of processes such as adeposition process, a lithography process, and an etching process. It isillustrated in conjunction with FIGS. 10 a-11 b and FIGS. 18 a-b.

Referring to FIGS. 10 a and 10 b, a material layer 226 is deposited overthe second spacer layer 222 and the material layer 224. A polishingprocess may be subsequently performed to the material layer 226. A hardmask layer 228 is deposited over the material layer 226. In anembodiment, the material layer 226 may be a Bottom Anti-ReflectiveCoating (BARC) layer while the hard mask layer 228 may be made ofsilicon. In another embodiment, instead of using two material layers 226and 228, one material layer may be used. A resist layer 230 is formed onthe hard mask layer 228, and is patterned with the second mask astrenches using a lithography process. In the present embodiment, thesecond mask includes three patterns, 230 a, 230 b, and 230 g, astrenches. The pattern 230 a overlaps with the first spacer features 220a and 220 b thereby defining trenches for the features 180 a, 182 a, and184 a (FIG. 2). The pattern 230 b overlaps with the first spacerfeatures 220 c and 220 d thereby defining trenches for the features 180b, 182 b, and 184 b (FIG. 2). These trench definitions are attributableto the dimensions and the pitch of the mandrel lines 218 a-d (FIG. 4 a),the first thickness T₁ (FIG. 5 b), and the second thickness T₂ (FIG. 8b). This point will be discussed in details in conjunction with FIG. 15.In the present embodiment, the spacing between the outer surfaces of thesecond spacer layer 222 disposed over the first spacer features 220 aand 220 b is tuned to be equal to the width, W₂, of the feature 182. Inanother embodiment as shown in FIGS. 18 a and 18 b, when the spacingbetween the outer surfaces of the second spacer layer 222 disposed overthe first spacer features 220 a and 220 b is greater than W₂, the secondmask includes six patterns 230 a-f. In this regard, FIG. 10 a may beviewed as a special case of FIG. 18 a where the patterns 230 a-c of FIG.18 a merge into the pattern 230 a of FIG. 10 a and the patterns 230 d-fof FIG. 18 a merge into the pattern 230 b of FIG. 10 a.

Referring to FIG. 10 c, the hard mask layer 228 is patterned by etchingthrough the openings of the patterned resist layer 230. In one example,the etching process includes applying a dry (or plasma) etch to removethe hard mask layer 228 within the openings of the patterned resistlayer 230. For example, a dry etching process may implement anoxygen-containing gas, a fluorine-containing gas (e.g., CF₄, SF₆, CH₂F₂,CHF₃, and/or C₂F₆), a chlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄,and/or BCl₃), a bromine-containing gas (e.g., HBr and/or CHBR₃), aniodine-containing gas, other suitable gases and/or plasmas, and/orcombinations thereof. In an embodiment, after the hard mask layer 228has been patterned, the patterned resist layer 230 is removed orpartially removed using a suitable process, such as wet stripping orplasma ashing.

Referring to FIG. 10 d, after the hard mask layer 228 has beenpatterned, the material layers 226 and 224 are etched with the patternedhard mask layer 228 as an etch mask using a suitable process, such as anetching process tuned to selectively remove the material layers 226 and224 while the second spacer layer 222 remains. In an embodiment, anyremaining portions of the resist layer 230 after the hard mask layer 228patterning step are also removed by such etching process. In anembodiment, any remaining portions of the hard mask layer 228 after thematerial layers 226 and 224 patterning step are also removed by suchetching process. The material layers 228 and 226 are removed thereafterusing a suitable process, such as an etching process tuned toselectively remove the material layers 228 and 226 while the materiallayer 224 and the second spacer layer 222 remain.

Referring to FIGS. 11 a and 11 b, trenches 232 a-g are formed into thematerial layer 224 and the second spacer layer 222 by the above etchingprocesses.

The method 100 (FIG. 1) proceeds to operation 118 by etching the secondspacer layer 222 to expose the material layer 216. Referring to FIGS. 12a and 12 b, the second spacer material disposed over the material layer216 is removed at the bottom of the trenches 232 a-g. The first spacerfeatures 220 a-d may also be exposed by the etching process and may bepartially removed. The material layer 224 may be partially removed bythe etching process. In an embodiment, the process of etching the secondspacer layer includes an anisotropic etch such as plasma etch. As aresult of the operation 118, the first and second spacer layers, 220 and222, and the material layer 224 are patterned with a plurality ofopenings and the plurality of openings corresponds to the features, 180a-b, 182 a-b, 184 a-b, and 186, of the target pattern 200 (FIG. 2).

The method 100 (FIG. 1) proceeds to operation 120 by transferring thepattern from the spacer layers, 220 and 222, and the material layer 224to the material layer 216 (FIGS. 13 a and 13 b) using a suitable processsuch as an anisotropic etching process. The spacer layers, 220 and 222,and the material layer 224 are thereafter removed (FIGS. 14 a and 14 b).Referring to FIGS. 14 a and 14 b, a pattern is formed in the materiallayer 216, matching the target pattern 200 (FIG. 2).

The method 100 (FIG. 1) proceeds to operation 122 to form a finalpattern or device with the patterned material layer 216. In anembodiment, a target pattern is to be formed as metal lines in amultilayer interconnection structure. For example, the metal lines maybe formed in an inter-layer dielectric (ILD) layer. In such a case, theoperation 122 forms a plurality of trenches in the ILD layer using thepatterned material layer 216; fills the trenches with a conductivematerial, such as a metal; and polishes the conductive material using aprocess such as chemical mechanical polishing to expose the patternedILD layer, thereby forming the metal lines in the ILD layer.

In another embodiment, the operation 122 forms fin field effecttransistor (FinFET) structures on a semiconductor substrate using thepatterned material layer 216. In this embodiment, the operation 122forms a plurality of trenches in the semiconductor substrate. Shallowtrench isolation (STI) features are further formed in the trenches by aprocedure that includes deposition to fill the trenches with adielectric material and polishing (such as CMP) to remove excessivedielectric material and to planarize the top surface of thesemiconductor substrate. Thereafter, a selective etch process is appliedto the dielectric material to recess the STI features, thereby formingfin-like active regions.

FIG. 15 illustrates the relationship among the various dimensions of thetarget pattern 200 (FIG. 2), the various dimensions of the mandrel lines218 a-d (FIG. 4 a), the thickness T₁ of the first spacer layer 220 (FIG.5 b), and the thickness T₂ of the second spacer layer 222 (FIG. 8 b).Referring to FIG. 15, which may be viewed as a part of the FIG. 13 arotated clockwise by 90 degrees, the various aforementioned dimensionshave the following:L _(m) =L+2×T ₂  (1)W _(1m) =W ₁+2×T ₂  (2)W _(3m) =W ₃+2×T ₂  (3)P _(m) =W ₁ +W ₂+2×T ₁+4×T ₂  (4)S ₁ ≧T ₁+2×T ₂  (5)S ₂ ≧T ₁+2×T ₂  (6)EtE=EtE_(m)+2×T ₂  (7)

The present disclosure provides various advantages over the traditionalspacer techniques where a pattern is trimmed before a spacer is formedover the pattern. One advantage is that a smaller EtE can be achieved bytuning the thickness T₂ By way of example, in a process P using thetraditional spacer techniques, the width of the mandrel lines 218 a-d isreduced by T in the trimming process so that the width meets a finalpattern pitch. The length of the mandrel lines 218 a-d is also reducedby approximately T by the same trimming process. Consequently, the endto end distance between the mandrel lines 218 a-d are increased fromEtE_(m) to (EtE_(m)+2×T) which is about the same as the end to enddistance of the final pattern by the process P. In contrast, in thepresent embodiment, the thickness T₂ can be tuned to be smaller than T,which indirectly reduces the end to end distance of the final pattern(see Equation (7) above). In addition to a reduced EtE distance, thewidth and length of the features 180 a-b, 182 a-b, and 184 a-b, of thetarget pattern 200 as well as the spacing among them can be made smallerby tuning the thickness T₁ and T₂. This generally provides benefits ofincreased pattern density. Another advantage of the present embodimentis cost saving because (1) the present embodiment avoids mandrel linetrimming processes and (2) the resist layer 218 (FIG. 4 b) can be madethinner.

The foregoing outlines features of several embodiments so that those ofordinary skill in the art may better understand the aspects of thepresent disclosure. Those of ordinary skill in the art should appreciatethat they may readily use the present disclosure as a basis fordesigning or modifying other processes and structures for carrying outthe same purposes and/or achieving the same advantages of theembodiments introduced herein. Those of ordinary skill in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the present disclosure, and that they may makevarious changes, substitutions, and alterations herein without departingfrom the spirit and scope of the present disclosure.

In one exemplary aspect, the present disclosure is directed to a methodof forming a target pattern for an integrated circuit (IC). The methodincludes forming a plurality of lines over a substrate with a firstmask; forming a first spacer layer over the substrate, over theplurality of lines, and onto sidewalls of the plurality of lines;removing at least a portion of the first spacer layer to expose theplurality of lines; removing the plurality of lines thereby providing apatterned first spacer layer over the substrate; forming a second spacerlayer over the substrate, over the patterned first spacer layer, andonto sidewalls of the patterned first spacer layer; and forming apatterned material layer over the second spacer layer with a second maskthereby the patterned material layer and the second spacer layercollectively define a plurality of trenches.

In another exemplary aspect, the present disclosure is directed to amethod of forming a pattern over a substrate having a plurality of hardmask layers. The method includes forming lines over the substrate;depositing a first material to a first thickness over the substrate,over the lines and onto sidewalls of the lines; removing the linesthereby providing a patterned first material over the substrate;depositing a second material to a second thickness over the substrate,over the patterned first material, and onto sidewalls of the patternedfirst material; depositing a third material over the second material;and patterning the second and third materials to form trenches.

In yet another exemplary aspect, the present disclosure is directed to amethod of forming a target pattern for an integrated circuit. The methodincludes decomposing the target pattern to at least a first mask, thefirst mask having a first mask pattern, and a second mask, the secondmask having a second mask pattern, wherein at least a portion of thefirst mask pattern overlaps with at least a portion of the second maskpattern. The method further includes patterning a substrate with thefirst mask thereby forming a first plurality of features; forming afirst spacer layer over the substrate, over the first plurality offeatures, and onto the sidewalls of the first plurality of features;partially removing the first spacer layer to expose the substrate andthe first plurality of features, and thereafter removing the firstplurality of features. The method further includes forming a secondspacer layer over the substrate, over the first spacer layer, and ontothe sidewalls of the first spacer layer; forming a first material layerover the second spacer layer; and patterning the first material layerwith the second mask wherein the second spacer layer and the patternedfirst material layer collectively define a second plurality of features.

What is claimed is:
 1. A method of forming a target pattern for anintegrated circuit, the method comprising: forming a plurality of linesover a substrate with a first mask; forming a first spacer layer overthe substrate, over the plurality of lines, and onto sidewalls of theplurality of lines; removing at least a portion of the first spacerlayer to expose the plurality of lines; removing the plurality of linesthereby providing a patterned first spacer layer over the substrate;forming a second spacer layer over the substrate, over the patternedfirst spacer layer, and onto sidewalls of the patterned first spacerlayer; and forming a patterned material layer over the second spacerlayer with a second mask, whereby the patterned material layer and thesecond spacer layer collectively define a plurality of trenches, andwherein the second spacer layer remains formed over the patterned firstspacer layer and on the sidewalls of the patterned first spacer layerafter the plurality of trenches are defined.
 2. The method of claim 1,further comprising: transferring the plurality of trenches to thesubstrate.
 3. The method of claim 1, further comprising: etching thesecond spacer layer through openings of the plurality of trenches toexpose the substrate; etching the substrate through the openings of theplurality of trenches; and after etching, removing the first spacerlayer, the second spacer layer, and the patterned material layer.
 4. Themethod of claim 1, wherein the forming the plurality of lines includes:forming a resist layer over the substrate; and patterning the resistlayer with the first mask.
 5. The method of claim 1, wherein the formingthe plurality of lines includes: forming a hard mask layer over thesubstrate; forming a resist layer over the hard mask layer; patterningthe resist layer with the first mask; etching the hard mask layer usingthe patterned resist layer as an etch mask; and thereafter removing thepatterned resist layer.
 6. The method of claim 1, wherein the formingthe first and second spacer layers includes deposition.
 7. The method ofclaim 1, wherein the forming the patterned material layer includes:forming a first material layer over the second spacer layer; forming asecond material layer over the first material layer and the secondspacer layer; patterning the second material layer with the second mask;etching the first material layer using the patterned second materiallayer as an etch mask; and thereafter removing the patterned secondmaterial layer.
 8. The method of claim 7, further comprising: etchingback the first material layer thereby to expose the second spacer layerbefore forming the second material layer.
 9. The method of claim 7,wherein the patterning the second material layer uses a photolithographyprocess including: forming a resist layer over the second materiallayer; patterning the resist layer with the second mask; etching thesecond material layer using the patterned resist layer as an etch mask;and thereafter removing the patterned resist layer.
 10. The method ofclaim 7, wherein the etching the first material layer includes a processselectively tuned to remove the first material layer using the patternedsecond material layer as an etch mask while the second spacer layerremains.
 11. The method of claim 1, wherein the removing at least aportion of the first spacer layer includes an anisotropic etchingprocess.
 12. The method of claim 1, wherein the removing the pluralityof lines includes a plasma etching process.
 13. The method of claim 1,wherein a dimension of at least one of the plurality of trenches isdefined, at least in part, by a pattern space of the first mask and athickness of the first and second spacer layers over the sidewalls ofthe plurality of lines.
 14. A method comprising: forming lines over asubstrate, the substrate having a plurality of hard mask layers;depositing a first material to a first thickness over the substrate,over the lines and onto sidewalls of the lines; removing the linesthereby providing a patterned first material over the substrate;depositing a second material to a second thickness over the substrate,over the patterned first material, and onto sidewalls of the patternedfirst material; depositing a third material over the second material;and patterning the second and third materials to form trenches, whereinthe second material remains deposited over the patterned first materialand on the sidewalls of the patterned first material.
 15. The method ofclaim 14, further comprising, before the depositing the first material:transferring the lines to one of the hard mask layers.
 16. The method ofclaim 14, further comprising, before the removing the lines, removing atleast a portion of the first material to expose the lines.
 17. Themethod of claim 14, further comprising, etching the substrate throughopenings of the trenches.
 18. A method of forming a target pattern foran integrated circuit, the method comprising: decomposing the targetpattern to at least a first mask, the first mask having a first maskpattern, and a second mask, the second mask having a second maskpattern, wherein at least a portion of the first mask pattern overlapswith at least a portion of the second mask pattern; patterning asubstrate with the first mask thereby forming a first plurality offeatures; forming a first spacer layer over the substrate, over thefirst plurality of features, and onto the sidewalls of the firstplurality of features; partially removing the first spacer layer toexpose the substrate and the first plurality of features; removing thefirst plurality of features; forming a second spacer layer over thesubstrate, over the first spacer layer, and onto the sidewalls of thefirst spacer layer; forming a first material layer over the secondspacer layer; and patterning the first material layer with the secondmask wherein the second spacer layer and the patterned first materiallayer collectively define a second plurality of features.
 19. The methodof claim 18, further comprising: etching back the first material layerto expose the second spacer layer before patterning the first materiallayer.
 20. The method of claim 18, further comprising: transferring thesecond plurality of features to the substrate; and thereafter removingthe patterned first material layer and the first and second spacerlayers.